This invention pertains to the art of a transport refrigeration system provided with control apparatus for reducing the probability of top freezing of fresh perishable cargo adjacent the path of refrigerated air discharged from the transport refrigeration unit.
In a trailer or truck hauling perishable food products, a part loss of the cargo occasionally occurs due to freezing the top of the load near the area where the cold air is blown out of the refrigeration unit. Typical practice in the art is to measure only the return air temperature at the inlet to the transport refrigeration unit without regard to the temperature of the air being blown out over the cargo. Thus, while the set point temperature of the unit might be of a value which would indicate top freezing should not occur, the actual temperature of the air being discharged from the unit may be at a significantly lower temperature than the set point temperature.
The related Barnett application discloses and claims a control scheme for reducing the likelihood of top freezing for a transport refrigeration unit of the character having a normal refrigerating capacity in one mode of operation and a reduced refrigerating capacity in another mode, in which time and temperature are effectively integrated so that with progressively lower discharge air temperatures, the period during which the unit operates with normal refrigerating capacity is progressively reduced with progressively lower temperatures.
It is the aim of my invention to provide one particular control arrangement including solid state circuitry for reducing the likelihood of top freezing.